This invention relates to a tetracarboxylic acid dianhydride having a disiloxane linkage and useful as an epoxy resin curing agent, more particularly to 1-(2,3-dicarboxyphenyl)-3-(3,4-dicarboxyphenyl)-1, 1,3,3-tetramethyldisiloxane dianhydride and a process for producing the same.
1,3-Bis(3,4-dicarboxyphenyl)-1,1,3,3-tetramethyldisiloxane dianhydride represented by the formula: ##STR1## has a melting point of 137.degree. C. to 138.degree. C. and is used as an epoxy resin curing agent to give a cured product excellent in adhesiveness and resistance to moisture. The above-mentioned symmetric compound can be synthesized as disclosed in J. Org. Chem. vol. 38, p 4271 (1973); "Polyimides" ed. by K. L. Mittal, vol. 1, p 51 (1984) published by Plenum Press Co.; and Japanese Patent Unexamined Publication No. 61-83191.
But since said compound has a melting point as high as 137.degree. to 138.degree. C., it is necessary to mix with an epoxy resin with heating. When a curing accelerator is added, there arise problems in that a pot life becomes very short, and gelation easily takes place at the time of mixing.